This application claims foreign priority to Japanese patent application no. 2001-219631 filed Jul. 19, 2001.
1. Field of the Invention
The present invention relates to a wet-slip resistant sheet and a wet-slip resistant structure. In particular, the present invention relates to a wet-slip resistant sheet comprising a substrate having a surface on which a plurality of tapered protrusions formed of a resin composition and being surrounded with a plurality of grooves which intersect each other, and a back surface opposing to the surface. This wet-slip resistant sheet has wet-slip resistance suitable for the application on floor surfaces.
The wet-slip resistant sheet of the present invention is useful as a slip-resistant sheet for a floor surface, which has an adhesive layer fixed to the back surface of the substrate and is fixed to a floor surface by the adhesive layer. In addition, the substrate is light-transmissive, and thus the wet-slip resistant sheet of the present invention is useful as a graphics-protective sheet which protects the graphics formed between the substrate and the floor surface. The graphics-protective sheet is particularly useful as a protective layer for a decorative sheet which has graphics fixed to the back surface of the substrate and decorates the floor surface.
2. Description of the Related Art
Hitherto, graphics are applied to a base film or a recording medium with a printing means such as an electrostatic printing method or an ink jet printing method, and the film or the medium having the applied graphics is used as a sign for advertising or guiding. The film or the medium having the graphics is fixed to the surface of a material such as a floor surface of a building by an adhesive layer which is provided on the back surface of the base film or the medium. To protect the graphics from damage, stain, etc., a graphics-protective sheet comprising a film or a sheet with a high light transmittance is laminated on the surface of the film or the substrate having the applied graphics. The graphics-protective sheet is adhered to the film or the substrate having the graphics by an adhesive layer, so that the graphics can be seen through the graphics-protective sheet.
A product such as the decorative sheet having the graphics protected with the protective sheet has been recently used as a decorative sheet for a floor surface. The decorative sheet for the floor surface is used by adhering it to a floor (or a material for constructing a floor) for simple repairing or as an advertising or guiding sign at a place having a relatively large number of passersby in a hotel, a shop, etc. Since the decorative sheet for the floor surface is used in such a way, it is required to have different properties than a decorative sheet for a signboard or a wall. One of such properties is wet-slip resistance on the surface of the sheet, since the decorative sheet for the floor surface should effectively prevent the slippage of the sole of a foot of the passerby (including a shoe""s sole) so that the passerby can walk on the sheet with no unusual feeling such as if the sheet were not fixed.
A nonslip sheet or a slip-resistant sheet which is fixed to the floor surface has a roughened surface and makes use of a gripping effect of protrusions formed by roughening. Many slip-resistant sheets are known, and are generally of two types. In one type, inorganic particles which form protrusions on the surface are dispersed and fixed, and in the other type, the sheet surface is roughened to form protrusions.
One example of the former type is a nonslip protective film comprising a soft synthetic resin containing fine particles added thereto as described in JP-A-2-144461, that is, a method for imparting the abrasion resistance and nonslip function to the film by adding hard particles such as alumina particles to the soft synthetic resin. However, in this method, the transparency of the protective film deteriorates unless the hard particles are transparent spherical particles (beads). Therefore, such a protective film is not useful as a graphics-protective sheet.
It is preferable to use the surface roughening method like in the above latter type so that the slip resistance of the surface of the protective sheet is enhanced without deteriorating the visibility of the graphics which is seen through the graphics-protective sheet. The graphics-protective sheet having the enhanced slip resistance and the decorative sheet which uses such a protective sheet are disclosed in U.S. Pat. No. 6,180,228 (corresponding to WO99/44840). This patent specification discloses a graphics article useful as a decorative sheet for a floor surface, that is, a graphics article comprising:
(a) a base film with a first major surface and a second major surface, a base film adhesive layer applied on the first major surface, wherein the base film adhesive layer comprises an adhesive composition selected such that the article will be removable from an outdoor surface, and an image layer applied to the second major surface of the base film; and
(b) a substantially clear graphics-protective sheet (which is named an image-protective top film in the U.S. patent) with a first major surface and a second major surface, a layer of a substantially clear adhesive on the first major surface, and wherein the second major surface of the image-protective layer is surface-roughened (embossed) to provide a BPN of at least 35 as measured by the procedures specified in ASTM E-303-93; wherein the graphics-protective sheet is attached to and overlies the base film and the image layer, and the image layer is visible through the graphics-protective sheet.
The image layer affords image information (visually displayed information such as an advertisement, a destination guides, etc.) to observers who see the graphics. The base film may be a vinyl resin film, a polyurethane film, etc., and the adhesive for the base film may be an acrylic adhesive. The clear adhesive for the graphics-protective sheet may be an acrylic pressure-sensitive adhesive.
Such a graphics article can construct an outdoor-advertising system when it is fixed to the floor surface. That is, passersby who walk on the graphics article fixed to the floor surface can see the image layer in good condition, and can walk on the graphics article with no unusual feeling such as if the article were not present.
U.S. Pat. No. 5,508,084 (corresponding to JP-A-10-502305) discloses a slip-resistant sheet having, on its surface, a plurality of tapered protrusions regularly arranged with a specific repeating pattern which are formed by surface roughening. The slip resistant sheet disclosed comprises a substrate having a surface and a back surface opposing to the surface, and a plurality of tapered protrusions of a resin composition, one end of each of which is bonded to the surface of the substrate. Each protrusion extends from one end to the other and is tapered towards the other end, and the tapered protrusions are regularly arranged on the surface of the substrate with a specific repeating pattern.
The above U.S. patent describes that a cubic structure such as a polygonal pyramid or a cone is preferable as the protrusion. The height of the protrusion is typically from 0.075 to 0.525 mm, preferably from 0.125 to 0.225 mm, most preferably 0.175 mm. The aspect ratio of the protrusion is usually from 0.1 to 5, and in the case of the polygonal pyramid, it is from 0.3 to 0.6. The aspect ratio (Asp) means the ratio of the protrusion""s height H to its equivalent base diameter (L) (Asp=H/L). This US patent describes that such a slip resistant sheet is useful as a mouse pad. Also, this US patent discloses that such a slip resistant sheet may be used in an airplane as a cover for a pull-down tray, or as a coaster for a drink container.
In the case of a wet-slip resistant sheet, the slip resistance in a wet state (under wet conditions) is preferably increased. When the slip resistant sheet is fixed to a floor surface of a building which directly or indirectly communicates with outdoors, passersby walk on the sheet in the undried state. Water from outdoors from, for example, rain or snow is conveyed onto the sheet spontaneously, or with moving bodies such as passersby, animals, goods, etc. The slip resistant sheet used on the floor surface should have an improved function to prevent the slippage of the sole of a foot of the passerby (including a shoe""s sole) on the sheet surface, that is, the improved wet-slip resistance. From such a viewpoint, the BPN value, which is measured according to ASTM E-303-93, should be at least 35 as disclosed in U.S. Pat. No. 6,180,228.
However, if the BPN value is too high, the clean recovery properties tend to decrease. In the case of the slip resistant sheet having a plurality of protrusions on its surface, the protrusions abrade the soles of the shoes and abrasion marks (sometimes called heel marks), which are formed of debris generated by abrading the soles of the shoes or the dirt from the soles of the shoes, tend to remain. When the BPN value is too high, the abrasion ability of the protrusions on the surface of the sheet is relatively high, and the abraded debris is easily captured in the grooves between the protrusions. Therefore, when the BPN is too high, the clean recovery properties are almost lost, and the abrasion marks may not be removed with a relatively simple cleaning method (such as cleaning with water using a brush). The rub-off stain due to the abrasion marks, which are barely removed, tends to be worse in the case of the pyramids (polygonal pyramids) or the cones having pointed apexes.
With the slip resistant sheet for the floor surface, it is important to control the BPN value in a specific range. Thus, the inventors initially attempted to optimally design the size of a protrusion using protrusions arranged along a regular pattern in order to control the BPN value. However, it was found that the size of the protrusion had no correlation with the BPN value and was not a good index for controlling the BPN value. Then, after further research and study, it was found that the BPN value can be controlled in the specific range, when a shape factor of the whole protrusions (PI, Profile Index) is controlled in a certain range.
Thus, an object of the present invention is to provide a wet-slip resistant sheet having a BPN value that can be easily controlled, and achieves the desired wet-slip resistance and clean recovery properties at the same time.
To solve the above problems, the present invention provides a wet-slip resistant sheet comprising a substrate having a front surface and a back surface opposing to the front surface, and a plurality of tapered protrusions of a resin composition, one end of each of which is bonded to the front surface of the substrate, wherein the tapered protrusions are regularly arranged on the front surface of the substrate with a specific repeating pattern and each of the protrusions is surrounded with a plurality of grooves which intersect each other, characterized in that an arrangement density (D) of the tapered protrusions is in the range between 50 protrusions/cm2 to 3,000 protrusions/cm2,
a profile index (PI) of the tapered protrusions is in the range of between 5 and 100, wherein the profile index (PI) is defined by the formula (1):
PI=Dxc3x97H2xe2x80x83xe2x80x83(1) 
in which D is an arrangement density of the tapered protrusions (unit: protrusions/cm2), and H is a height of the tapered protrusion (unit: mm),
and a wet-slip resistance number (a British Pendulum Tester number (BPN)), which is measured according to ASTM E-303-93, is at least 35.